Overlaminating adhesive films have been used to protect a printed surface produced by thermal transfer printing, ink-jet printing, offset-printing, letterpress printing, gravure printing, etc., from damages by water, sunlight, scratches, etc. The overlaminating adhesive films generally comprise a surface base material in the form of a transparent film, a release material and an adhesive layer sandwiched therebetween. The release material is peeled off from the films upon use.
The adhesives used in the overlaminating adhesive films include various adhesives of an emulsion type, a solvent type, a solvent-free type, etc. which are made of rubber-based, acrylic or vinyl ether-based compounds. Among these adhesives, the acrylic adhesives are more suitably used because the adhesives of this type are excellent in weather resistance, peeling stability with time and transparency. In particular, special attention has been recently paid to emulsified acrylic adhesives since the adhesives contain no organic solvent harmful to human bodies and, therefore, are favorable to environments (for example, refer to Japanese Patent Application Laid-open Nos. 2001-240819 and 2002-80809).
However, in general, the emulsion-type adhesives are considerably deteriorated in water whitening resistance and water adhesion resistance as compared to those of the solvent type adhesives. Also, when the above acrylic emulsion-type adhesive is used to produce an overlaminating adhesive film by a so-called transfer-coating method in which the adhesive is applied on a release material and then a transparent film is laminated over the adhesive, it is required that an additive for improving the wettability such as surfactant is added to the adhesive in order to enhance a wettability of the adhesive to the release material. The addition of the additive, however, causes deterioration in water resistance of the resultant adhesive film. In particular, in the case where the overlaminating adhesive film is laminated over an ink-jet printed surface, there arises such a problem that the printed surface suffers from ink bleeding when preserved under humidified conditions.